Chemical modification of graphene with a thermotropic liquid crystalline polymer and its reinforcement effect in the polymer matrix

In our work, graphene oxide (GO) was covalently functionalized with propargyl alcohol to obtain alkyne terminated graphene oxide. These alkyne groups on graphene oxide sheets further reacted with a kind of azido-functionalized liquid crystalline polymer via click chemistry, which was found to be a facile and effective method to graft the liquid crystalline polymer onto GO sheets. The liquid crystalline polymer introduced here was a side-chain liquid crystalline polymer - poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl] styrene} (PMPCS). Azido-functionalized PMPCS was prepared beforehand by atom transfer polymerization to obtain polymers with designed molecular weight. The successful introduction of functional PMPCS chains onto GO sheets was confirmed by FTIR, TEM and AFM characterizations. Thermogravimetric analysis was used to calculate the graft efficiency. Raman and X-ray photoelectron spectroscopies revealed that functional PMPCS had more profound p-p stacking interactions and charge transfer effect with GO sheets after liquid crystalline phase transition. Therefore, the as-prepared GO-PMPCS composite had potential applications in improving the mechanical properties of liquid crystalline PMPCS matrix as had been investigated by rheological measurements.